In metal components used in automobiles, high accuracy is required. For improving the accuracy of the metal components, it is necessary for burrs generated by processing to be reliably removed by polishing. In the related art, for removing the burrs of a workpiece metal component, a brush that is formed by bundling a plurality of linear abrasive materials in which resin binder is impregnated and cured in fibrous alumina is generally used. In order to remove the burrs, the brush is rotated while tips of the abrasive materials of the brush come into contact with a surface of the workpiece metal component.
A polishing machine capable of stably exerting performance of a brush-shaped grindstone by setting a cutting amount of work of the brush-shaped grindstone using alumina to be constant is disclosed in JP 2005-111640A (Reference 1). In the polishing machine, a tool holding body holding the brush-shaped grindstone using alumina is movably supported in a direction toward the work (workpiece metal component) to a holder body and a direction away from the work, and is biased by a predetermined biasing force toward the work by a compression coil spring. Thus, even if the brush-shaped grindstone is worn, since the tool holding body is moved toward the work by the compression coil spring and a position of the tip of the brush-shaped grindstone is constantly maintained, a cutting load of the brush-shaped grindstone to the work, that is, a reaction force received from the work, is constant and the cutting amount toward the work can be constantly maintained.
In the polishing machine described in Reference 1, the brush-shaped grindstone is biased by the compression coil spring. The brush-shaped grindstone is configured of a brush case and a brush-shaped grindstone body inserted therein. The brush-shaped grindstone body is configured of a plurality of linear abrasive materials in which binder resin is impregnated and cured in set yarns of alumina and a cylindrical holder that collectively holds a base end side of the linear abrasive materials. The polishing is performed by protruding tips of the linear abrasive materials from a lower end of the brush case and moving the tips of the linear abrasive materials while the tips come into contact with the surface of the work, and the burrs are removed. The burrs are removed and thereby the tips of the linear abrasive materials are worn.
Since the brush case and the brush-shaped grindstone body are integrally moved, as a number of polishing times increases, a protruding length of the linear abrasive materials protruding from the lower end of the brush case is shortened due to wear. Thus, after a predetermined number of removal times have elapsed, it is necessary to stop the polishing machine and to manually protrude the linear abrasive materials from the lower end of the brush case, and therefore complete automation of a polishing process is not achieved. Furthermore, in order to stably perform the polishing, the cutting load toward the work has to be constant, but a practical cutting load is changed by a compression length of the compression coil spring. In order to make the cutting load constant, before the polishing process is started, it is necessary to abut the brush-shaped grindstone to a master work and adjust a height of the brush-shaped grindstone. Thus, time for adjusting the cutting load is necessary in addition to the practical polishing time for the time of the polishing process and it takes much extra time. As described above, in a structure of the brush-shaped grindstone, there is room for further improvement.